Radio wave control element

Abstract

The invention provides a radio wave control element which can shorten switching time and has low radio wave loss. A radio wave control element having a first electrode, a liquid crystal composition layer, and a second electrode, the radio wave control element having a metasurface structure in which a plurality of fine structures are arranged, the metasurface structure constituting at least a portion of the first electrode, and having an intermediate layer between the liquid crystal composition layer and one of the first electrode and the second electrode, the intermediate layer has a maximum refractive index change of 0.001 (1 / V) or less per unit voltage in radio waves having a wavelength in the range of 300 [mu] m to 30 cm.

Description

Technical Field

[0001] This invention relates to an electromagnetic wave control element. Background Technology

[0002] High-frequency radio waves (millimeter waves, terahertz waves) required for high-capacity wireless communication have high linearity. Therefore, radio wave control elements are needed to bend the direction of radio wave propagation into arbitrary directions.

[0003] However, for example, the reflection direction of radio waves by a typical reflector is constant, and the reflection direction is a normal reflection with the incident angle and the exit angle being equal. Therefore, the range of changing the direction of radio wave travel is greatly limited, and there is a problem that it is difficult to transmit radio waves to the desired location.

[0004] In contrast, an electromagnetic wave control element is proposed, which is configured as a structure in which a liquid crystal layer is disposed between a metasurface structure made of conductors and conductors (electrodes). By changing the voltage applied between the two conductors, the refractive index of the liquid crystal layer is changed, thereby changing the directivity of the electromagnetic wave.

[0005] For example, Patent Document 1 describes a structure comprising: a first conductor; a plurality of second conductors, which are opposite to and repeatedly arranged with respect to the first conductor; a plurality of third conductors, which are respectively opposite to the plurality of second conductors; a dielectric constant variable layer disposed between at least one of the plurality of third conductors and the plurality of second conductors and between the plurality of third conductors and the first conductor, wherein the dielectric constant changes with voltage; and a fourth conductor that connects the first and second conductors to a second conductor located next to the first and second conductors.

[0006] Previous technical documents Patent documents Patent Document 1: International Publication No. 2011 / 152055 Summary of the Invention

[0007] The technical problem to be solved by the invention In radio wave control devices, it is desirable to shorten the switching time when changing the directionality of radio waves. In the radio wave control device described above, where a liquid crystal layer is disposed between conductors, the switching time can be shortened by reducing the thickness of the liquid crystal layer. However, if the liquid crystal layer is made thinner, there is a problem of increased radio wave loss.

[0008] In view of the above, the objective of the present invention is to provide a radio wave control element that can shorten the switching time and reduce radio wave loss.

[0009] means for solving technical problems In order to solve the above-mentioned problems, the inventors conducted in-depth research and discovered that the following structure can solve the problems.

[0010] [1] An electromagnetic wave control element comprising a first electrode, a liquid crystal composition layer, and a second electrode, wherein, The radio wave control element has a metasurface structure composed of multiple microstructures arranged in a row. The metasurface structure constitutes at least a portion of the first electrode. An intermediate layer is provided between one of the first electrode and the second electrode and the liquid crystal composition layer, wherein the maximum refractive index change per unit voltage in the intermediate layer in the range of 300 μm to 30 cm is less than 0.001 (1 / V).

[0011] [2] According to the radio wave control element described in [1], the second electrode has a waveguide for guiding radio waves on the side opposite to the liquid crystal composition layer side, and the second electrode has an opening through which the radio waves pass.

[0012] [3] According to the radio wave control element described in [2], the second electrode also serves as a waveguide.

[0013] [4] The radio wave control element according to any one of [1] to [3], wherein, The thickness of the intermediate layer is 0.1 to 2 times that of the liquid crystal composition layer.

[0014] [5] The radio wave control element according to any one of [1] to [4] controls radio waves in the range of 300 μm to 30 cm.

[0015] Invention Effects According to the present invention, a radio wave control element that can shorten the switching time and reduce radio wave loss can be provided. Attached Figure Description

[0016] Figure 1 This is a diagram illustrating an example of the use of a radio wave control element.

[0017] Figure 2 This is a diagram illustrating an example of a metasurface structure used in radio wave control elements.

[0018] Figure 3 This diagram illustrates the mechanism by which the emission direction of radio waves is altered in radio wave control elements.

[0019] Figure 4 This is a diagram that conceptually illustrates an example of the radio wave control element of the present invention.

[0020] Figure 5 This is a diagram that conceptually represents an example of a liquid crystal alignment pattern in a radio wave control element.

[0021] Figure 6 It is a graph showing the relationship between the applied voltage and the amount of phase delay of the radio wave.

[0022] Figure 7 This is a diagram that conceptually represents another example of a radio wave control element.

[0023] Figure 8 yes Figure 7 A three-dimensional diagram of the radio wave control element shown. Detailed Implementation

[0024] The present invention will now be described in detail.

[0025] The following description of the constituent elements is based on a representative embodiment of the present invention, but the present invention is not limited to this embodiment.

[0026] In addition, in this specification, the numerical range indicated by “~” represents the range including the values ​​recorded before and after “~” as the lower and upper limits.

[0027] Furthermore, in this specification, "horizontal" and "vertical" do not mean horizontal and vertical in the strict sense, but rather refer to the range of ±5° horizontally and ±5° vertically, respectively.

[0028] Furthermore, in this specification, each component may be described using a single equivalent substance or in combination of two or more substances. In cases where two or more substances are used in combination for each component, unless otherwise specified, the content of that component refers to the total content of the combined substances.

[0029] Unless otherwise specified, the bonding direction of the divalent groups (e.g., -CO-O-, etc.) described in this specification is not limited. For example, in the case where Y is -CO-O- in a compound represented by the formula "XYZ", the compound can be either "XO-CO-Z" or "X-CO-OZ".

[0030] [Radio wave control components] The radio wave control element of the present invention has a first electrode, a liquid crystal composition layer, and a second electrode, wherein, The radio wave control element has a metasurface structure composed of multiple microstructures arranged in a row. The metasurface structure constitutes at least a portion of the first electrode. An intermediate layer is provided between one of the first electrode and the second electrode and the liquid crystal composition layer, wherein the maximum refractive index change per unit voltage in the intermediate layer in the range of 300 μm to 30 cm is less than 0.001 (1 / V).

[0031] The radio wave control element of the present invention operates on radio waves (electromagnetic waves). Examples of radio waves include those with frequencies of 1 GHz to 1000 GHz and wavelengths of 300 μm to 30 cm. Radio waves in this frequency band are also referred to as high-frequency radio waves (centimeter waves, millimeter waves, terahertz waves), which are capable of high-capacity wireless communication and have high linearity.

[0032] In the radio wave control element of the present invention, by applying a voltage between the first electrode and the second electrode, the orientation state of the liquid crystal compound contained in the liquid crystal composition layer is controlled, and the refractive index anisotropy of the liquid crystal composition layer is adjusted, thereby enabling the adjustment of the propagation direction of the radio wave.

[0033] The following description uses accompanying drawings to illustrate specific examples of radio wave control elements.

[0034] exist Figure 1 The radio wave reflecting device 2 shown uses the radio wave control element 10, which is based on the technology of this invention. The radio wave reflecting device 2 is capable of reflecting radio waves RW, which have high directivity, radiated from the antenna ANT located behind the building BL, toward the area AR1 in front of the building BL, which is shadowed when viewed from the antenna ANT.

[0035] Furthermore, the radio wave reflecting device 2 can change the reflection direction of the radio wave RW in different directions in multiple regions AR1 and AR2. For example, if users utilizing wireless communication are mostly located in region AR1 during the daytime and mostly in region AR2 during the nighttime, the areas where users are concentrated sometimes change according to the time of day. In this case, the radio wave reflecting device 2 can change the area supplying the radio wave RW by changing the reflection direction of the radio wave RW according to the time of day.

[0036] like Figure 2 As shown, the radio wave control element 10 is a reflective radio wave control element having a metasurface structure 12 and reflecting the travel direction of the radio wave RW in the desired direction.

[0037] The metasurface structure 12 is a structure utilizing metamaterials. Metamaterials are artificial materials that exhibit properties not found in natural materials, such as a negative refractive index for electromagnetic waves. The electromagnetic wave control element 10 is a structure formed by arranging multiple unit cells UC in a two-dimensional manner. The two-dimensional plane formed by the arrangement of multiple unit cells UC becomes the reflecting surface of the electromagnetic wave RW. Each unit cell UC contains a microstructure 14 as a metamaterial, which constitutes the smallest unit on the reflecting surface capable of dynamically changing the phase of the electromagnetic wave RW. As an example, the microstructure 14 is made of metal. The microstructure 14 is on the order of the wavelength of the incident electromagnetic wave RW and functions as a resonator that resonates through interaction with the incident electromagnetic wave RW. Electrically, the microstructure 14 can be considered, for example, equivalent to a resonant circuit in which an alternating current resonates by connecting a coil and a capacitor in series. Through the resonance of the microstructure 14, the phase of the incident electromagnetic wave RW changes. Furthermore, by dynamically changing the resonance conditions of the microstructure 14 through various methods, the phase delay of the radio wave RW can also be controlled.

[0038] The radio wave control element 10 primarily operates on radio waves with frequencies ranging from 1 GHz to 1000 GHz (1 THz). Therefore, in the radio wave control element 10, the metasurface structure 12 is configured to operate on radio waves with frequencies ranging from 1 GHz to 1000 GHz. For example, the wavelength of radio waves with frequencies ranging from 1 GHz to 1000 GHz is 300 μm to 30 cm, and the size of the microstructure 14 constituting the metasurface structure 12 is approximately half the wavelength. By setting the size of the microstructure 14 to be below the wavelength of the radio wave RW, the microstructure 14 resonates through the transmitted radio wave RW, functioning as a phase modulation element that modulates the phase of the radio wave RW.

[0039] exist Figure 3 In the example shown by the incident direction IN and the exit direction OUT, the overall travel direction of the radio wave RW can be considered as the normal direction relative to the straight line connecting the wavefronts of the multiple radio waves RW. Furthermore, consider the case in the radio wave control element 10 where, for example, the phase delay of the radio wave RW incident on and reflected to each of the multiple one-dimensionally arranged unit cells UC gradually increases from the right-hand unit cell UC towards the left-hand unit cell UC. In this way, even when the straight line connecting the wavefronts of the individual incident radio waves RW is parallel to the reflecting surface, the straight line connecting the wavefronts of the individual radio waves RW reflected in each unit cell UC will be tilted relative to the reflecting surface. That is, the travel direction of the radio wave RW emitted from the reflecting surface, i.e., the exit direction OUT, only changes by an angle θ relative to the incident direction IN of the radio wave RW. Thus, by controlling the phase delay for each unit cell UC, the travel direction of the radio wave RW can be controlled.

[0040] As a result, in a conventional reflector, the direction of travel of the radio wave RW can only be changed to the direction of positive reflection, while the radio wave reflecting device 2, by using the metasurface structure 12, can change the direction of travel of the radio wave RW to a direction other than positive reflection. Furthermore, by dynamically changing the phase retardation in each unit cell UC, the direction of travel of the radio wave RW can be dynamically changed.

[0041] As an example, such as Figure 4 As conceptually shown, the radio wave control element 10 uses a liquid crystal composition layer 20 as a means to dynamically change the resonance conditions of the microstructures 14 of the metasurface structure 12. The radio wave control element 10, from bottom to top, includes a second electrode 26, an intermediate layer 32, a liquid crystal composition layer 20, and a metasurface structure 12. The second electrode 26, the liquid crystal composition layer 20, and the intermediate layer 32 are disposed on a support 24.

[0042] Each unit cell UC comprises a microstructure 14, a liquid crystal composition layer 20, an intermediate layer 32, and a second electrode 26. The microstructure 14 is provided individually for each unit cell UC. The liquid crystal composition layer 20, intermediate layer 32, support 24, and second electrode 26 are not independent structures for each unit cell UC, but are integrally formed with regions corresponding to multiple unit cells UC.

[0043] In the radio wave control element 10, the second electrode 26 is bonded to the support 24, the second electrode 26 is bonded to the intermediate layer 32, and the intermediate layer 32 is bonded to the liquid crystal composition layer 20 as needed using adhesives. There are no limitations on the bonding method; various methods using OCA (Optical Clear Adhesive) that can transmit the radio waves targeted by the radio wave control element 10, and other known methods that can transmit the radio waves targeted by the radio wave control element 10, can be used.

[0044] As an example, the microstructure 14 is formed of a conductive material and also serves as the first electrode forming an electrode pair with the second electrode 26.

[0045] Furthermore, a power supply 28 for applying a voltage between the microstructure 14 and the second electrode 26 is connected to each microstructure 14. Therefore, the magnitude of the voltage applied to each unit cell UC can be controlled. The second electrode 26 is a common electrode shared by all unit cells UC, while each microstructure 14 of each unit cell UC functions as an individual electrode. The second electrode 26, functioning as a common electrode, is an example of the "second electrode" according to the technology of this invention, while the individual electrode also used by the microstructure 14 is an example of the "first electrode." The microstructure 14 as the first electrode and the second electrode 26 as the second electrode are an example of an "electrode pair for applying voltage."

[0046] There is no particular limitation on the voltage application mechanism that applies voltage to each microstructure 14, for example, TFT (thin film transistor).

[0047] The radio wave control element 10 is a reflective type, and the second electrode 26 also serves as a reflective layer for the reflected radio wave RW.

[0048] The alignment state (hereinafter also referred to as alignment pattern) of the liquid crystal compound LC in the liquid crystal composition layer 20 changes when a voltage is applied. The arrangement direction of the microstructures 14 in each unit cell UC is a direction orthogonal to the thickness direction (Z direction in the figure) of the liquid crystal composition layer 20 (X direction or Y direction in the figure). Here, the microstructures 14 and the second electrode 26 are respectively disposed on opposite sides of the liquid crystal composition layer 20 in the thickness direction. By supplying power from the power source 28 to the microstructures 14 and the second electrode 26, a voltage is applied between the microstructures 14 and the second electrode 26 in each unit cell UC. By applying the voltage, an electric field is generated in the thickness direction of the liquid crystal composition layer 20, thereby changing the alignment state of the liquid crystal compound LC in each unit cell UC. Furthermore, by adjusting the voltage applied to each unit cell UC, the alignment state of the liquid crystal compound LC in each unit cell UC can be adjusted.

[0049] exist Figure 5 In the example shown, the liquid crystal compound LC is a rod-shaped liquid crystal compound with a long axis and a short axis. As an example, when no voltage is applied between the microstructure 14, which acts as an electrode pair, and the second electrode 26, no electric field is generated in the liquid crystal composition layer 20. In this state, as... Figure 5 As conceptually shown in the preceding paragraph, the liquid crystal compound LC is oriented with its long axis along the thickness direction of the liquid crystal composition layer 20. In the following description, this orientation is also referred to as "vertical orientation".

[0050] Furthermore, the thickness direction is the stacking direction of the microstructure 14 (first electrode), the liquid crystal composition layer 20, the intermediate layer 32, and the second electrode 26. Also, the main surface is the largest surface of the sheet-like object (film, plate, layer), typically both sides of the sheet-like object in the thickness direction.

[0051] If a voltage is applied between the microstructure 14 and the second electrode 26 from this state, an electric field is generated in the liquid crystal composition layer 20, thereby changing the orientation state of the liquid crystal compound LC. Specifically, as Figure 5 As conceptually shown in the lower paragraph, the orientation state of the liquid crystal compound LC in the region corresponding to the microstructure 14 changes according to the magnitude of the applied voltage, tilting relative to the thickness direction of the liquid crystal composition layer 20. Figure 5In the example shown in the lower paragraph, the tilt angle of the liquid crystal compound LC is maximized. In the maximized tilt angle state, the liquid crystal compound LC is oriented with its major axis perpendicular to the thickness direction of the liquid crystal composition layer 20. In the following description, the orientation state with the tilt angle maximized is also referred to as "horizontal orientation".

[0052] The greater the tilt of the liquid crystal compound LC, that is, the closer the long axis of the liquid crystal compound LC is to the main surface direction of the liquid crystal composition layer 20 (in Figure 5 The greater the refractive index of the liquid crystal composition layer 20 (where the angle is in the X or Y direction), the greater the refractive index. Conversely, the smaller the tilt of the liquid crystal compound LC, i.e., the closer the long axis of the liquid crystal compound LC is to the thickness direction of the liquid crystal composition layer 20 (the Z direction in the figure), the smaller the refractive index of the liquid crystal composition layer 20. Through such changes in the refractive index of the liquid crystal composition layer 20 in each unit cell UC, the resonance condition of the microstructure 14 changes, and the phase retardation of the incident electromagnetic wave RW changes. In this example, Figure 5 The phase delay of the lower segment of the unit cell UC is compared to Figure 5 The upper segment of the unit cell has a large UC.

[0053] That is, if the orientation state of the liquid crystal compound LC changes at the position corresponding to the microstructure 14 in each unit cell UC and in the liquid crystal composition layer 20 surrounding it, the refractive index of the liquid crystal composition layer 20 relative to the electromagnetic wave RW transmitted through each unit cell UC changes. Furthermore, since the refractive index is positively correlated with the dielectric constant, the resonant condition of the microstructure 14, which functions as a resonator, changes due to the change in the refractive index of the liquid crystal composition layer 20. This change in the resonant condition of the microstructure 14 manifests as a change in the phase retardation of the electromagnetic wave RW. Therefore, by changing the refractive index of the liquid crystal composition layer 20, the phase retardation of the electromagnetic wave RW can be changed. Moreover, the change in the refractive index of the liquid crystal composition layer 20 itself also causes a change in the phase retardation of the electromagnetic wave RW. The refractive index of the liquid crystal composition layer 20 in each unit cell UC changes according to the voltage V applied to each unit cell UC; therefore, as an example, the relationship between voltage V and the phase retardation of the electromagnetic wave RW is as follows: Figure 6 As shown.

[0054] like Figure 3As shown, if an electromagnetic wave RW is incident on the electromagnetic wave control element 10 from the microstructure 14 side, the electromagnetic wave RW sequentially passes through the microstructure 14 and the liquid crystal composition layer 20. Furthermore, the electromagnetic wave RW is reflected at the second electrode 26, which also acts as a reflective layer, and again sequentially passes through the liquid crystal composition layer 20 and the microstructure 14 before exiting from the electromagnetic wave control element 10. The electromagnetic wave RW is reflected through this incident / exit path. In the incident / exit path, for the electromagnetic wave RW that passes through each unit cell UC, phase modulation is generated due to the resonance of the microstructure 14 and phase modulation is generated due to the transmission of the liquid crystal composition layer 20. More specifically, in each unit cell UC, the resonance condition of the microstructure 14 is determined according to the refractive index of the liquid crystal composition layer 20, and phase modulation of the electromagnetic wave RW is generated through resonance corresponding to this condition. Furthermore, phase modulation of the electromagnetic wave RW corresponding to the magnitude of the refractive index of the liquid crystal composition layer 20 is also generated.

[0055] according to Figure 6 The relationship shown is that the applied voltage V controls the phase delay of the radio wave RW by a certain amount per unit cell UC, thereby controlling the reflection direction of the radio wave RW reflected in the radio wave control element 10.

[0056] Also Figure 3 As shown, in a conventional reflector, the direction of travel of the radio wave RW can only be changed to the direction of positive reflection. However, in the radio wave control element 10, by using the metasurface structure 12, the direction of travel of the radio wave RW can be changed to a direction other than positive reflection. Furthermore, by dynamically changing the phase retardation in each unit cell UC, the direction of travel of the radio wave RW can be dynamically changed.

[0057] Furthermore, the control of the direction of travel of the radio wave RW emitted from the radio wave control element 10, in addition to, Figure 3 As shown in the example, in addition to controlling the reflected radio wave RW to travel in a straight line in one direction, various other examples are considered. For example, the radio wave RW emitted from the radio wave control element 10 can be focused toward a certain focal point or diverge in the opposite direction. The direction of travel of the emitted radio wave RW can be controlled by adjusting the voltage applied to each unit cell UC to adjust the amount of phase delay of the radio wave RW in each unit cell UC.

[0058] For example, consider the following situation: Figure 3As shown, in the case of multiple unit cells UC arranged in one direction, the phase retardation of the central unit cell UC is increased, while the phase retardation is decreased towards both sides. In this case, if the wavefronts of the radio waves RW transmitted through each unit cell UC form a V-shape, the emitted radio waves RW can be focused. Conversely, consider the case where the phase retardation of the central unit cell UC is decreased, while the phase retardation is increased towards both sides. In this case, if the wavefronts of the radio waves RW transmitted through each unit cell UC form a mountain shape (inverted V-shape), the emitted radio waves RW can be diverged. The degree of focusing and divergence can also be adjusted by controlling the phase retardation of the radio waves RW transmitted through each unit cell UC by adjusting the magnitude of the applied voltage.

[0059] Similar to known metasurface structures, the metasurface structure 12 is formed by a two-dimensional arrangement of microstructures 14 as a metamaterial. In the metasurface structure 12 illustrated in the figure, as... Figure 2 As shown, the microstructures 14 are arranged in a two-dimensional pattern at equal intervals in the X and Y directions, which are orthogonal to each other. Furthermore, in this metasurface structure 12, all microstructures 14 are identical, as an example. The metasurface structure 12 constitutes at least a portion of the first electrode. That is, as described above, the plurality of microstructures 14 constituting the metasurface structure 12 are the first electrodes in each unit cell UC. Furthermore, the metasurface structure 12 (microstructures 14) can be supported by a support.

[0060] There are no limitations on the support for the microstructure 14. As long as it can support the microstructure 14 and transmit radio waves RW with a frequency of 1 GHz to 1000 GHz targeted by the radio wave control element 10, various known sheet materials can be used. Examples of supports include metal substrates with oxide insulating layers such as silicon substrates containing silicon oxide, supports made of oxides such as silicon oxide, supports made of semiconductors such as germanium and chalcogenide glass, polyacrylic resin films such as polymethyl methacrylate, cellulose resin films such as cellulose triacetate, cyclic olefin polymer films (e.g., those manufactured under the trade name "ARTON" by JSR Corporation, and those manufactured under the trade name "ZEONOR" by Zeon Corporation), polyethylene terephthalate (PET) films, polycarbonate films, and polyvinyl chloride films, as well as glass plates.

[0061] There are no restrictions on the thickness of the support, as long as it can support the microstructure 14 and achieve sufficient transmittance for radio waves RW with frequencies from 1 GHz to 1000 GHz, and thus achieve sufficient strength depending on the application of the radio wave control element 10. The thickness of the support can be appropriately set according to the material in which the support is formed to meet these conditions.

[0062] Furthermore, in the radio wave control element 10 according to the technology of this invention, a support is not a necessary structure for the metasurface structure 12, and a support may be omitted. For example, if possible, the metasurface structure 12 may be formed by directly arranging microstructures 14 on the surface of the liquid crystal composition layer 20. When a support is present, it may be a structure with a support between the metasurface structure 12 and the liquid crystal composition layer 20, or it may be a structure with a support on the side of the metasurface structure 12 opposite to the side of the liquid crystal composition layer 20.

[0063] As described above, the metasurface structure 12 is a structure formed by separating and arranging the microstructures 14, which are metamaterials, in a two-dimensional plane. More specifically, it is basically composed of the arrangement of unit cells UC, which are units of a microstructure 14 and the space surrounding the microstructure 14.

[0064] In the radio wave control element 10 according to the technology of the present invention, the morphology of the metasurface structure is substantially the same as that of known metasurface structures. Therefore, various known metasurface structures can be utilized in the radio wave control element 10 according to the technology of the present invention.

[0065] That is, in the technology of the present invention, there are no limitations on the shape and forming material of the microstructure 14, the arrangement of the microstructure 14, and the spacing of the microstructure 14. Furthermore, the metasurface structure 12 can be designed using known methods based on the wavelength of the radio wave RW controlled by the radio wave control element 10 and the target reflection characteristics (e.g., the range of controllable reflection directions). For example, the amplitude and phase of the radio wave RW reflected by the microstructure 14 can be calculated using commercially available simulation software, and the arrangement of the microstructure 14 can be set in a manner that becomes the distribution of the target phase modulation amount. Regarding phase modulation, in the case of using the liquid crystal composition layer 20 as in this example, it is generated based on the refractive index and the interaction between the refractive index and the microstructure 14, and the phase modulation amount is determined based on the resonance characteristics of the microstructure 14, which change according to the refractive index.

[0066] The radio wave control element 10 according to the present invention controls radio waves with frequencies ranging from 1 GHz to 1000 GHz. Therefore, in the metasurface structure 12, a microstructure 14 is selected to impart a desired phase difference to the radio waves with that frequency, and the arrangement of the microstructures is then determined. Specifically, when the radio waves with frequencies ranging from 1 GHz to 1000 GHz are controlled, the wavelength range of the radio waves is approximately 300 μm to 30 cm; therefore, the size of the microstructure 14 is also selected to be within this wavelength range.

[0067] While the number of microstructures 14 in a unit cell UC is generally one, the present invention is not limited to this. That is, in the radio wave control element involved in the present invention, a unit cell UC can have multiple microstructures 14 as needed, depending on the reflection characteristics, the size of the microstructures 14, the forming material and shape, and the size of the unit cell UC. In this case, a unit cell UC can have different microstructures 14. However, the unit cell UC is the smallest unit capable of dynamically changing the phase of the radio wave RW; therefore, even when a unit cell UC has multiple microstructures 14, the phase modulation amount is determined for each unit cell UC.

[0068] Furthermore, the material used to form the microstructure 14 is not limited, and various materials known for their use as microstructures in metasurface structures can be used. Examples of materials for forming the microstructure 14 include metals and dielectrics. In the case of metals, copper, gold, and silver are preferred examples from the viewpoint of low optical loss. Furthermore, composites composed of metal particles and binders, as well as oxide semiconductors, can also be used as materials for forming the microstructure 14. On the other hand, in the case of dielectrics, silicon, titanium oxide, and germanium are preferred examples considering their high refractive index and ability to increase phase modulation. Additionally, as... Figure 4 As shown, when the microstructure 14 also serves as an electrode in an electrode pair with the second electrode 26, the microstructure 14 is formed of a conductor.

[0069] Similarly, the shape of the microstructure 14 is not limited, and various shapes used as microstructures in known metasurface structures can be utilized. Examples include: a cross-shaped solid where cuboids intersect; a cuboid shape; a cylindrical shape; a V-shaped solid where cuboids are connected at the ends, as shown in Japanese Patent Application Publication No. 2018-046395; a roughly H-shaped solid, such as an H-beam; and a roughly C-shaped solid, such as a C-channel. Furthermore, as shown in Japanese Patent Application Publication No. 2018-046395, the V-shaped solid and the cross-shaped solid can utilize various shapes by adjusting the angle formed by two cuboids. In addition, shapes such as those described in "Appl.Sci.2018,8(9),1689;https: / / doi.org / 10.3390 / app8091689" can also be used. Figure 5 The solid shown has a base shape, etc.

[0070] In the metasurface structure 12, the microstructures 14 can be of the same type, or multiple types of microstructures 14 can be used in combination. Furthermore, the same microstructures 14 can be arranged in the same orientation or in different orientations in the XY plane. Also, microstructures 14 with the same orientation and microstructures 14 with different orientations can coexist. However, in the radio wave control element 10 according to the technology of this invention, it is preferable to use only one type of microstructure 14, and to arrange all microstructures 14 in the same orientation.

[0071] And, as Figure 3 As shown, the preferred embodiment of the metasurface structure 12 is a two-dimensional arrangement of identical microstructures 14, all having the same structure, at equal intervals in the orthogonal X and Y directions. However, the invention is not limited to this; as described above, various microstructures can be used together, and the spacing and arrangement of the microstructures 14 can also differ in the planar direction. However, considering the controllability of the reflection direction of the electromagnetic wave RW when a voltage is applied to the liquid crystal composition layer 20, it is preferable to use identical microstructures 14 for the metasurface structure 12. Furthermore, it is more preferable that the spacing between the microstructures 14 is equal, and even more preferably that they are equally spaced in both the orthogonal X and Y directions.

[0072] The liquid crystal composition layer 20 is a layer formed by aligning the liquid crystal compound LC in a predetermined state. As described above, the orientation state of the liquid crystal compound LC changes when a voltage is applied.

[0073] In the state where no voltage is applied, Figure 4 The liquid crystal compound LC in the liquid crystal composition layer 20 illustrated is vertically oriented. When a voltage is applied to the liquid crystal composition layer 20, the liquid crystal compound LC tilts in the thickness direction according to the voltage and becomes horizontally oriented at most. In addition, in the radio wave control element 10, the orientation of the liquid crystal compound LC is not limited to changing from vertical orientation to horizontal orientation or vice versa; it can also change from a state tilted relative to the thickness direction to horizontal or vertical orientation, or from horizontal or vertical orientation to a state tilted relative to the thickness direction, or the angle can change from a state tilted relative to the thickness direction to a state tilted relative to the thickness direction.

[0074] Furthermore, the liquid crystal composition layer 20 may be formed on the surface of the alignment film described later, for example, by a known method.

[0075] In the radio wave control element 10, the liquid crystal composition layer 20 is stacked on the second electrode 26 or the intermediate layer 32 on the support 24. The support 24 is substantially the same as the support described above.

[0076] Here, when the liquid crystal composition layer 20 is formed on the second electrode 26 or the intermediate layer 32, an alignment film for aligning the liquid crystal compound LC to a predetermined state can be provided on the surface of the second electrode 26 or the intermediate layer 32. Various known alignment films can be used. Examples include a rubbing film composed of organic compounds such as polymers, a tilted vapor-deposited film of inorganic compounds, a film with microgrooves, and a film formed by accumulating organic compounds such as ω-trisanoic acid, dioctadecylmethylammonium chloride, and methyl stearate using the Langmuir-Blodgett (LB) method. Furthermore, so-called photo-aligned films, which are formed by irradiating polarized or unpolarized light onto a light-oriented raw material, can also be used as alignment films. These alignment films can be formed using known methods corresponding to the forming material of the substrate.

[0077] Alternatively, in the case of a support having a microstructure 14, the liquid crystal composition layer 20 may be formed on the support.

[0078] The liquid crystal composition containing the liquid crystal compound LC used to form the liquid crystal composition layer 20 will be described later.

[0079] The entire surface of the support 24 on the side of the liquid crystal composition layer 20 is covered by the second electrode 26. The second electrode 26 is an electrode that changes the orientation of the liquid crystal compound LC in the liquid crystal composition layer 20, and as described above, it also functions as a reflective layer for reflecting radio waves RW with frequencies of 1 GHz to 1000 GHz incident from the metasurface structure 12 side. In the example shown, the second electrode 26 is arranged between the support 24 and the liquid crystal composition layer 20, but it is not limited to this; the second electrode 26 may also be arranged on the side of the support 24 opposite to the side of the liquid crystal composition layer 20.

[0080] The second electrode 26 is not limited; as long as it has sufficient conductivity and can reflect electromagnetic waves RW, it can be made of a sheet of various known materials.

[0081] As an example of the second electrode 26, examples include metal layers such as copper, aluminum, gold, and silver; inorganic conductive materials such as ITO (indium tin oxide); organic conductive materials such as polythiophene, represented by PEDOT (poly(3,4-ethylenedioxythiophene)); and graphene. Inorganic conductive materials, organic conductive materials, and graphene are transparent to visible light, but they function as reflective layers for electromagnetic waves of the aforementioned frequencies.

[0082] There is no limitation on the thickness of the second electrode 26, as long as the thickness is appropriately set according to the forming material of the second electrode 26 to reflect the electromagnetic waves to the target with the required reflectivity.

[0083] As described above, the radio wave control element 10 according to the present invention is a reflective radio wave control element having a metasurface structure 12 and a liquid crystal composition layer 20. In the radio wave control element 10, by supplying power to each microstructure 14, the orientation state of the liquid crystal compound LC in the corresponding region of the liquid crystal composition layer 20 is changed, forming regions with different refractive indices according to each unit cell UC, thereby reflecting the radio wave RW in the desired direction. Furthermore, by changing the power supplied to each microstructure 14, i.e., the voltage applied to the liquid crystal composition layer 20, the reflection direction of the incident radio wave RW can be switched.

[0084] In the radio wave control element 10 according to the technology of the present invention, the refractive index anisotropy Δn of the liquid crystal composition layer 20 for radio waves is not limited, but a larger one is preferred. Here, in the reflective radio wave control element 10 of this example, the refractive index anisotropy Δn of the liquid crystal composition layer 20 for radio waves of 100 GHz is preferably 0.35 or more. From the viewpoint that by setting the refractive index anisotropy Δn of the liquid crystal composition layer 20 for radio waves of 100 GHz to 0.35 or more, the liquid crystal composition layer 20 can be made thinner, and the switching of the reflection direction of radio waves RW can be performed more quickly, this is preferred.

[0085] Furthermore, there is no limitation on the thickness of the liquid crystal composition layer 20, as long as the thickness is appropriately set according to the forming material of the liquid crystal composition layer 20 to impart the required phase difference to the radio wave RW. Here, as will be described later, the radio wave control element 10 according to the technology of the present invention has an intermediate layer 32 whose refractive index does not change. Therefore, by making the liquid crystal composition layer 20 thinner, the time for switching the reflection direction of the incident radio wave RW is shortened, that is, the response speed is accelerated, and the radio wave RW loss can also be reduced. Considering this, the thickness of the liquid crystal composition layer 20 is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. From the viewpoint that by setting the thickness of the liquid crystal composition layer 20 to 200 μm or less, the switching of the reflection direction of the radio wave RW can be performed more quickly, this is preferable.

[0086] Furthermore, the Δn (birefringence) of the liquid crystal composition layer 20 is not limited, but a larger value is preferred. The Δn of the liquid crystal composition layer is preferably 0.35 or more. This is preferred from the viewpoint that by setting the Δn of the liquid crystal composition layer to 0.35 or more, the liquid crystal composition layer can be made thinner, allowing for more rapid switching of the direction of radio wave propagation.

[0087] The intermediate layer 32 is a layer in which the maximum refractive index change per unit voltage in an electromagnetic wave with a wavelength range of 300 μm to 30 cm is less than 0.001 (1 / V). That is, the intermediate layer 32 is a layer in which the refractive index does not change due to voltage. Furthermore, the intermediate layer 32 is an insulating layer. The maximum refractive index change per unit voltage of the intermediate layer 32 in an electromagnetic wave with a wavelength range of 300 μm to 30 cm is preferably 0.0005 (1 / V).

[0088] In this invention, the maximum refractive index change per unit voltage in radio waves with wavelengths ranging from 300 μm to 30 cm is determined by terahertz time-domain spectroscopy (THz-TDS).

[0089] First, the intermediate layer was cut into 10mm × 10mm test pieces with a thickness of 1mm. Next, tin oxide (SnO2) films were formed on both sides of the intermediate layer using a sputtering method. Then, a transmission-type terahertz spectroscopic optical system was fabricated. Under conditions of 25°C and 10%RH, the refractive index of the test piece was measured by observing the time-varying waveform of the photoelectric field when a voltage was applied to the tin oxide film during transmission.

[0090] In the case of a liquid crystal composition layer, firstly, the liquid crystal composition is encapsulated in a glass cell (10 mm × 10 mm, 1 mm thick) with a tin oxide (SnO2) film formed by sputtering as an electrode. Next, an optical system for transmission-type terahertz spectroscopy is fabricated, and the refractive index of the liquid crystal composition encapsulated in the glass cell is measured based on the change in the time waveform of the photoelectric field of the test piece when a voltage is applied to the transmission electrode at 25°C and 10% RH.

[0091] The intermediate layer 32 only needs to be disposed between one of the microstructure 14 (first electrode) and the second electrode 26 and the liquid crystal composition layer 20. That is, as shown... Figure 4 As shown, the second electrode 26, the intermediate layer 32, and the liquid crystal composition layer 20 are arranged sequentially. Alternatively, the second electrode 26, the liquid crystal composition layer 20, and the intermediate layer 32 may also be arranged sequentially.

[0092] Furthermore, the radio wave control element 10 may have two or more intermediate layers 32. For example, an intermediate layer may be provided between the microstructure 14 (first electrode) and the liquid crystal composition layer 20, and between the liquid crystal composition layer 20 and the second electrode 26.

[0093] Furthermore, the alignment film used to align the aforementioned liquid crystal compound LC to a predetermined state can be designated as the intermediate layer 32.

[0094] There are no particular limitations on the material used to form the intermediate layer 32; a dielectric is preferred, as long as it has sufficient transmittance to radio waves RW. Examples include semiconductors such as silicon, silicon dioxide (quartz (SiO2)), germanium, and chalcogenide glass; polyacrylic resins such as polymethyl methacrylate; cellulose resins such as cellulose triacetate; cyclic olefin polymers; polyethylene terephthalate (PET); polycarbonate and polyvinyl chloride resins; and glass.

[0095] As described above, in an electromagnetic wave control element that places a liquid crystal composition layer between a metasurface structure (first electrode) and a second electrode, and controls the reflection direction of the electromagnetic wave RW by applying different voltages to each cell corresponding to a plurality of microstructures constituting the metasurface structure, thereby causing the refractive index of the liquid crystal composition layer in each cell to differ, it is required to shorten the switching time when changing the reflection direction of the electromagnetic wave RW. In such an electromagnetic wave control element, by reducing the thickness of the liquid crystal composition layer, the change in the orientation state of the liquid crystal compound when the voltage is applied can be performed quickly. That is, by reducing the thickness of the liquid crystal composition layer, the switching time of the reflection direction of the electromagnetic wave RW in the electromagnetic wave control element can be shortened.

[0096] However, it is known that if the liquid crystal composition layer is made thinner, there is a problem of increased radio wave RW loss during reflected radio waves. The inventors conducted research on this issue and found that if the distance between the metasurface structure (first electrode) and the second electrode is shortened, the radio wave RW absorption based on the liquid crystal composition increases, leading to increased radio wave RW loss.

[0097] In contrast, the radio wave control element 10 of the present invention has an intermediate layer 32 between one of the metasurface structure 12 (first electrode) and the second electrode 26 and the liquid crystal composition layer 20. This intermediate layer 32 has a maximum refractive index change of 0.001 (1 / V) or less per unit voltage in radio waves with wavelengths ranging from 300 μm to 30 cm. Therefore, even when the liquid crystal composition layer 20 is thinned, the distance between the first electrode and the second electrode 26 can be increased. Thus, the radio wave control element 10 of the present invention can reduce the thickness of the liquid crystal composition layer, shorten the switching time of the reflection direction of the radio wave RW in the radio wave control element, and suppress the absorption of the radio wave RW to reduce radio wave RW loss.

[0098] From the viewpoint of shortening the switching time of the reflection direction of radio wave RW (improving response speed) and reducing radio wave RW loss, the thickness of the intermediate layer 32 is preferably 0.1 to 2 times the thickness of the liquid crystal composition layer 20, more preferably 0.2 to 1.8 times, and even more preferably 0.5 to 1.5 times.

[0099] Furthermore, there are no particular limitations on the dielectric constant of the material constituting the intermediate layer 32 relative to the applied voltage. As in the case where the second electrode 26 of the wave control element 10 and the microstructure 14 are electrodes, when the liquid crystal composition layer and the intermediate layer are arranged in series between opposing electrodes, the higher the dielectric constant of the intermediate layer, the more effectively the electric field applied to the liquid crystal composition layer can be increased, and therefore this is preferred.

[0100] In the example described above, the radio wave control element 10 reflects the radio wave RW and controls the reflection direction of the radio wave RW. However, the radio wave control element of the present invention is not limited to this.

[0101] Figure 7 This is a diagram that conceptually illustrates another example of the radio wave control element of the present invention. Furthermore, Figure 8 yes Figure 7 A three-dimensional diagram of the radio wave control element shown.

[0102] Figure 7 and Figure 8 The radio wave control element 50 shown in the figure, from bottom to top, includes a waveguide 52, an intermediate layer 32, a liquid crystal composition layer 20, and a metasurface structure 12 (microstructure 14). The intermediate layer 32 and the liquid crystal composition layer 20 are disposed on a portion of the outer surface of the waveguide 52. Figure 7 and Figure 8 In the radio wave control element 50 shown, the waveguide 52 is a waveguide made of conductors such as metal, and the waveguide also serves as the second electrode.

[0103] In addition, Figure 7 and Figure 8 In the radio wave control element 50 shown, for the... Figure 4 The same symbols are used to mark the same parts of the radio wave control element 10 shown. The following description mainly focuses on the different parts. Furthermore, in... Figure 7 and Figure 8 The diagram of the support body is omitted in the radio wave control element 50 shown, but it may have a support body.

[0104] In the example shown, waveguide 52 is a cylindrical component with a rectangular cross-section, and is a metal waveguide that guides the radio wave RW within its hollow section. The radio wave RW propagates within waveguide 52 while generating an electromagnetic field corresponding to the shape, size, wavelength (frequency) of waveguide 52.

[0105] Furthermore, the waveguide 52 has a plurality of openings 54 on the wall portion of the side where the intermediate layer 32, the liquid crystal composition layer 20 and the microstructure 14 are stacked, that is, the surface opposite to the microstructure 14 that functions as the second electrode, connecting the cavity portion to the outside. The openings 54 are respectively provided at positions corresponding to the unit cell UC (i.e., the microstructure 14).

[0106] Waveguide 52 has multiple openings 54, and radio waves RW guided within the hollow portion of waveguide 52 seep out through the openings 54 and are released to the outside. At this time, the radio waves RW pass through the intermediate layer 32 and the liquid crystal composition layer 20. In the radio wave control element 50, also... Figure 4 Similarly, the radio wave control element 10 shown can control the travel direction of the radio wave RW by controlling the phase delay amount, i.e., by performing phase modulation on each unit cell UC. That is, the radio wave control element 50 can control the emission direction of the radio wave RW. Furthermore, by activating the phase delay amount in each unit cell UC, the emission direction of the radio wave RW can be activatingly changed.

[0107] Here, the radio wave control element 50 of the present invention has an intermediate layer 32 between one of the waveguides 52, which function as the metasurface structure 12 (first electrode) and the second electrode, and the liquid crystal composition layer 20. This intermediate layer 32 has a maximum refractive index change of 0.001 (1 / V) or less per unit voltage in radio waves with wavelengths ranging from 300 μm to 30 cm. Therefore, even when the liquid crystal composition layer 20 is thinned, the distance between the first electrode and the second electrode can be increased. Thus, the radio wave control element 50 of the present invention can reduce the thickness of the liquid crystal composition layer, shorten the switching time of the emission direction of the radio wave RW in the radio wave control element, and suppress the absorption of the radio wave RW to reduce radio wave RW loss.

[0108] In addition, Figure 8 In the example shown, the cross-sectional shape of waveguide 52 is set to a rectangle, but it is not limited to this and can be set to various shapes such as square, circle, polygon, etc.

[0109] Furthermore, the dimensions of waveguide 52 are not particularly limited. The length of waveguide 52 is preferably 1 to 10,000 mm, and more preferably 3 to 3,000 mm.

[0110] And, as Figure 7 and Figure 8 In the example shown, where waveguide 52 also serves as the second electrode, waveguide 52 can be formed from the same material (conductor) as the material used to form the second electrode 26 described above.

[0111] Furthermore, in Figure 7 and Figure 8In the example shown, the waveguide 52 is configured to also serve as the second electrode, but this is not a limitation; the waveguide and the second electrode can be separate components. When the waveguide and the second electrode are separate, the waveguide is positioned on the side of the second electrode opposite to the liquid crystal composition layer. In the case of separate waveguide and second electrode, the second electrode also has an opening at a position corresponding to each unit cell through which the radio wave RW passes. Furthermore, an exit portion for emitting the radio wave RW is provided in the waveguide at a position corresponding to the opening of the second electrode.

[0112] When the waveguide and the second electrode are separate, in addition to waveguides formed by the aforementioned conductors, waveguides that can guide electromagnetic waves, such as stripline lines, microstrip lines, and coplanar lines, can also be appropriately utilized.

[0113] Furthermore, the size of the opening formed in the second electrode is preferably 0.01 to 100,000 mm. 2 More preferably, it is 0.02 to 80000 mm. 2 More preferably, it is 0.05 to 50000 mm. 2 .

[0114] Furthermore, in the example shown in the figure, the opening formed on the second electrode is set to a structure in which one opening is provided in each unit cell UC, but it is not limited to this, and more than two openings may be provided in each unit cell UC.

[0115] Furthermore, the radio wave control element can have a temperature adjustment component that adjusts the temperature of the liquid crystal composition layer. In this case, the orientation state of the liquid crystal compound in the liquid crystal composition layer can be fixed. This method will be described in detail below.

[0116] Regarding the temperature adjustment component, its structure is not particularly limited as long as it is a component that adjusts the temperature of the liquid crystal composition layer 20. The placement of the temperature adjustment component is also unrestricted, as long as it can adjust the temperature of the liquid crystal composition layer 20. The temperature adjustment component can be arranged in a layered manner between any of the components constituting the radio wave control element, or it can be placed outside the radio wave control element.

[0117] Furthermore, the temperature adjustment component may include a heating device for increasing the temperature of the liquid crystal composition layer 20 and a cooling device for decreasing the temperature of the liquid crystal composition layer 20.

[0118] The steps for fixing the orientation state of the liquid crystal compound in the liquid crystal composition layer 20 using an electromagnetic control element with a temperature adjustment component are as follows. Furthermore, the liquid crystal compound included in the liquid crystal composition layer 20 is a compound that exhibits liquid crystal properties when heated by the temperature adjustment component. Specifically, a composition that exhibits a nematic phase at any temperature between 50 and 150°C and exhibits a glassy state or a smectic phase at any temperature below 50°C is preferably used.

[0119] First, in the radio wave control element, the liquid crystal composition layer 20 is heated by a temperature adjustment component and transformed into a liquid crystal phase. Next, while maintaining the heating process, a voltage is applied between the second electrode 26 and the microstructure 14 to control the orientation direction of the liquid crystal compound. At this time, the voltage applied per unit cell UC can be varied to create different orientation states of the liquid crystal compound. Afterward, if the heating and heating processes are stopped, the orientation state of the liquid crystal compound is fixed below the liquid crystal phase transition temperature. That is, the orientation state of the liquid crystal compound can be maintained even without applying a voltage.

[0120] Furthermore, depending on the type of liquid crystal compound used, a state with higher orientation can be generated in the radio wave control element. For example, when the liquid crystal compound displays a nematic phase and a higher-order liquid crystal phase such as a smectic phase, the higher-order liquid crystal phase can be fixed by rapidly cooling the radio wave control element using a temperature adjustment component.

[0121] The materials used to form the liquid crystal composition layer will be described below.

[0122] The liquid crystal composition layer is formed from a liquid crystal composition containing liquid crystal compounds, and the orientation state of the liquid crystal compounds contained in the liquid crystal composition layer changes according to the magnitude of the applied voltage. Furthermore, the liquid crystal composition may contain other components besides liquid crystal compounds. Moreover, the liquid crystal composition preferably does not substantially contain solvent. "Substantially does not contain solvent" means that the solvent content is 5% by mass or less, preferably 1% by mass or less, relative to the total mass of the liquid crystal composition.

[0123] The liquid crystal composition preferably displays a nematic phase over the entire temperature range of 10 to 50°C. Furthermore, the liquid crystal composition preferably displays a nematic phase at any temperature between 50 and 150°C, and exhibits a glassy state or smectic liquid crystal properties at any temperature below 50°C.

[0124] Furthermore, the liquid crystal composition preferably contains an azo compound, and the liquid crystal compound is preferably a liquid crystal compound having an azo structure. By including an azo compound in the liquid crystal composition, the Δn (birefringence) of the liquid crystal composition layer can be increased. Therefore, in order to impart the desired refractive index, i.e., the desired phase difference, to the radio wave, the required thickness of the liquid crystal composition layer can be made thinner. By making the liquid crystal composition layer thinner, the orientation of the liquid crystal compound changes more rapidly when the applied voltage is changed. As a result, the response speed to changes in the voltage applied to the liquid crystal composition layer can be accelerated, and the switching of the travel direction of the incident radio wave can be performed in a shorter time.

[0125] There are no particular restrictions on the number of azo compounds, as long as they contain an azo structure (-N=N-). There are no particular restrictions on the number of azo structures a compound can have, as long as it has 1 or more, preferably 2 or more. There is no particular upper limit on the number of azo structures, but it is more common to find compounds with 5 or fewer, and even more common to find compounds with 3 or fewer.

[0126] The azo compound can be a liquid crystal compound or a non-liquid crystal compound, but is preferably a liquid crystal compound. That is, the azo compound is preferably a liquid crystal compound having an azo structure.

[0127] As an azo compound, the compound represented by formula (1) is preferred.

[0128] [Chemical Formula 1] In equation (1), Ar 1 This represents an aromatic ring with a valence of (m1+1).

[0129] The aromatic ring with the (m1+1) valence mentioned above can be a monocyclic ring or a fused ring with two or more rings. Alternatively, the aromatic ring can be a ring formed by multiple monocyclic rings bonded together by single bonds (e.g., biphenyl ring, terphenyl ring).

[0130] Examples of aromatic rings with the aforementioned (m1+1) valence include aromatic hydrocarbon rings or aromatic heterocycles.

[0131] Examples of aromatic hydrocarbon rings include benzene rings, naphthalene rings, anthracene rings, fluorene rings, biphenyl rings, and anthracene rings. Among these, benzene rings are preferred.

[0132] Examples of aromatic heterocycles include pyridine rings, thiophene rings, quinoline rings, isoquinoline rings, and thiazole rings.

[0133] For example, when m1 is 1, Ar 1 This indicates a divalent aromatic ring.

[0134] In equation (1), Ar 2 Aromatic rings with a valence of (m2+2).

[0135] The aromatic ring with the (m2+2) valence mentioned above can be a monocyclic ring or a fused ring with more than two rings. Alternatively, the aromatic ring can be a ring formed by multiple monocyclic rings bonded together by single bonds (e.g., biphenyl ring, terphenyl ring).

[0136] Examples of aromatic rings with the aforementioned (m2+2) valence include aromatic hydrocarbon rings or aromatic heterocycles.

[0137] Examples of aromatic hydrocarbon rings include benzene rings, naphthalene rings, anthracene rings, fluorene rings, biphenyl rings, and anthracene rings. Among these, benzene rings are preferred.

[0138] Examples of aromatic heterocycles include pyridine rings, thiophene rings, quinoline rings, isoquinoline rings, and thiazole rings.

[0139] For example, when m2 is 1, Ar 2 This indicates a trivalent aromatic ring.

[0140] In equation (1), Ar 3 This represents an aromatic ring with a valence of (m3+1).

[0141] The aromatic ring with the (m3+1) valence mentioned above can be a monocyclic ring or a fused ring with two or more rings. Alternatively, the aromatic ring can be a ring formed by multiple monocyclic rings bonded together by single bonds (e.g., biphenyl ring, terphenyl ring).

[0142] As an aromatic ring with the aforementioned (m3+1) valence, examples include aromatic hydrocarbon rings or aromatic heterocycles.

[0143] Examples of aromatic hydrocarbon rings include benzene rings, naphthalene rings, anthracene rings, fluorene rings, biphenyl rings, and anthracene rings. Among these, benzene rings are preferred.

[0144] Examples of aromatic heterocycles include pyridine rings, thiophene rings, quinoline rings, isoquinoline rings, and thiazole rings.

[0145] For example, when m3 is 1, Ar 3 This indicates a divalent aromatic ring.

[0146] In equation (1), R 1 R 2 and R 3 Substituents are represented independently.

[0147] When m1≥2, multiple R 1 Multiple Rs can be the same or different. When m² ≥ 2, multiple Rs... 2 Multiple Rs can be the same or different, provided that m³ ≥ 2. 3 They can be the same or different.

[0148] The aforementioned substituents are monovalent substituents, and examples include alkyl, alkenyl, aralkyl, aryl, heterocyclic, halogen, cyano, nitro, mercapto, hydroxyl, alkoxy, aryloxy, alkylthio, arylthio, acyloxy, amino, alkylamino, dialkylamino, carboxamide, sulfonamide, aminosulfonylamino, oxycarbonylamino, oxysulfonylamino, urea, thiourea, acyl, oxycarbonyl, carbamoyl, sulfonyl, sulfinyl, aminosulfonyl, carboxyl (including salts), sulfonyl (including salts), and groups formed by combining these groups. These groups can be further substituted by these groups.

[0149] In equation (1), m1, m2 and m3 each independently represent integers from 0 to 5. m1 is preferably 1 to 3, m2 is preferably 0 to 1, and m3 is preferably 1 to 3.

[0150] In formula (1), n1 represents an integer from 1 to 4, preferably from 1 to 3, and more preferably from 2 to 3.

[0151] Furthermore, the liquid crystal composition preferably contains a dichroic pigment, and the liquid crystal compound is also preferably a liquid crystal dichroic pigment. By orienting the dichroic pigment in the liquid crystal composition, the anisotropy of the refractive index to electromagnetic waves can be further increased.

[0152] Dichroic pigments are substances that exhibit dichroism, which means that the absorbance varies depending on the polarization direction.

[0153] Dichroic pigments can be used alone or in combination with two or more. Preferably, the liquid crystal composition contains two or more dichroic pigments. When the liquid crystal composition contains two or more dichroic pigments, it is preferable to contain two to four dichroic pigments, and more preferably two to three dichroic pigments.

[0154] Dichroic pigments preferably exhibit liquid crystal properties. That is, liquid crystal dichroic pigments are preferred.

[0155] From the viewpoint of achieving better results with the present invention, the preferred dichroic pigment is a compound represented by formula (X).

[0156] [Chemical Formula 2] In equation (X), R 1 and R 2 Each of the following can be independently represented as a straight-chain or branched hydrocarbon group having 1 to 10 carbon atoms. The hydrocarbon group may contain oxygen, nitrogen, or sulfur atoms.

[0157] The number of carbon atoms in the above-mentioned hydrocarbon group is 1 to 10, and from the viewpoint of better effect of the present invention, it is preferably 1 to 8, and more preferably 2 to 6.

[0158] The aforementioned hydrocarbon group is either straight-chain or branched, preferably straight-chain.

[0159] The hydrocarbons mentioned above can be saturated hydrocarbon groups or unsaturated hydrocarbon groups.

[0160] The aforementioned hydrocarbon group may contain oxygen, nitrogen, or sulfur atoms. The aforementioned hydrocarbon group may contain multiple atoms selected from the group consisting of oxygen, nitrogen, and sulfur atoms.

[0161] For example, the aforementioned hydrocarbon group may contain -O-, -S-, -CO-, -CS-, -CO-O-, or -CO-NR between carbon-carbon atoms or at the end. 10 -、-NR 10 - or groups formed by combining them.

[0162] R 10 It represents a hydrogen atom or an alkyl group.

[0163] As the aforementioned hydrocarbon group, it is preferable that it may contain -O-, -S-, -CO-, -CS-, -CO-O-, or -CO-NR between carbon-carbon atoms or at the end. 10 -、-NR 10 - or alkyl groups that combine them.

[0164] In equation (X), R 1 and R 2 They can bond together to form a ring.

[0165] The resulting ring can be either an aliphatic ring or an aromatic ring.

[0166] In equation (X), A and B independently represent divalent aromatic cyclic groups.

[0167] Examples of divalent aromatic cyclic groups include divalent aromatic hydrocarbon cyclic groups or divalent aromatic heterocyclic groups.

[0168] A divalent aromatic hydrocarbon cyclic group is a group formed by removing two hydrogen atoms from an aromatic hydrocarbon ring. The aromatic hydrocarbon ring can be a monocyclic or fused ring. Examples of such aromatic hydrocarbon rings include benzene rings, naphthalene rings, anthracene rings, pyrene rings, phenanthrene rings, and fluorene rings.

[0169] A divalent aromatic heterocyclic group is a group formed by removing two hydrogen atoms from an aromatic heterocycle. The aforementioned aromatic heterocycle can be a monocyclic or a fused ring. Examples of aromatic heterocycles include pyridine rings, pyrimidine rings, pyridazine rings, pyrazine rings, triazine rings (e.g., 1,2,3-triazine rings, 1,2,4-triazine rings, and 1,3,5-triazine rings), tetrazine rings (e.g., 1,2,4,5-tetraazine rings), quinoxaline rings, pyrrole rings, furan rings, thiophene rings, imidazole rings, oxazole rings, thiazole rings, benzopyrrole rings, benzofuran rings, benzothiophene rings, benzoimidazolium rings, benzoxazole rings, benzothiazole rings, benzoxazole rings, naphthopyrrole rings, naphthofuran rings, naphthothiophene rings, naphthoimidazolium rings, naphthooxazole rings, pyrroloimidazolium rings (e.g., 5H-pyrrolo[1,2-a]imidazolium rings), imidazoxazole rings (e.g., imidazo[2,1-b]oxazole rings), and thieno[2,1-b]oxazole rings. 3-d]thiazole ring, benzothiadiazole ring, benzodithiophene ring (e.g., benzo[1,2-b:4,5-b']dithiophene ring, thieno[3,2-b]thiophene ring, thiazo[5,4-d]thiazo[2,3-b:6,7-b']thiophene ring, naphtho[2,3-b:6,7-b']thiophene ring, benzo[3,2-b]thiophene ring, thiazo[5,4-d]thiazo[5,4-d]thiazo[5,4-b ... [Dithiophene ring, naphtho[2,1-b:6,5-b']dithiophene ring, naphtho[1,2-b:5,6-b']dithiophene ring and 1,8-dithiabicyclopentane[b,g]naphthylene ring, etc.), benzothiophene and benzothiophene ring, dithiophene[3,2-b:2',3'-d]thiophene ring and 3,4,7,8-tetrathiabicyclopentane[a,e]cyclopentadiene ring.

[0170] In formula (X), L represents a single bond, -CR=CR-, -C≡C-, -CR=N-, or -N=N-.

[0171] R can independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms.

[0172] In equation (X), n represents an integer from 1 to 3. When n is 2 or 3, there are multiple A and L that can be the same or different.

[0173] R 3 It represents a hydrogen atom or a substituent.

[0174] There are no particular restrictions on the types of substituents, such as halogen atoms (e.g., fluorine, chlorine, bromine, and iodine atoms), hydrocarbon groups (alkyl (including cycloalkyl, bicycloalkyl, and tricycloalkyl), alkenyl (including cycloalkenyl and bicycloalkenyl), alkynyl, and aryl), heterocyclic groups, cyano, isothiocyanate groups, nitro, alkoxy, aryloxy, silyl, silanoxy, heterocyclic, acyloxy, carbamoyloxy, alkoxycarbonyloxy, and aryloxycarbonyl. alkyl oxy, primary amino, secondary or tertiary amino (including aniline), alkyl thio, aryl thio, heterocyclic thio, alkyl or aryl sulfinyl, alkyl or aryl sulfonyl, acyl, aryloxy carbonyl, alkoxy carbonyl, aryl or heterocyclic azo, imide, phosphin, oxophosphin, oxophosphinyloxy, oxophosphinylamino, phosphonyl, carboxyl, phosphate, sulfonic acid, hydroxyl, thiol, amide, carbamoyl, urea, borate, and groups formed by combining them.

[0175] Preferably, the substituents are alkyl, alkoxy, cyano, or isothiocyanate groups that may contain oxygen, nitrogen, or sulfur atoms. The alkyl group may contain oxygen, nitrogen, or sulfur atoms. For example, the alkyl and alkoxy groups may contain -O-, -S-, -CO-, -CS-, -CO-O-, or -CO-NR between carbon atoms. 10 -、-NR 10 - or groups formed by combining them. R 10 It represents a hydrogen atom or an alkyl group.

[0176] The aforementioned alkyl and alkoxy groups may include multiple -O-, -S-, -CO-, -CS-, -CO-O-, -CO-NR 10 -、-NR 10 - or groups formed by combining them.

[0177] There is no particular limitation on the number of carbon atoms in the alkyl and alkoxy groups mentioned above, but it is preferably 1 to 10, and more preferably 1 to 6.

[0178] R represents a hydrogen atom or an alkyl group.

[0179] The total content of dichroic pigments in the liquid crystal composition is 30% by mass or more relative to the total mass of the liquid crystal composition. Furthermore, when the liquid crystal composition contains only one dichroic pigment, the total content of the dichroic pigment is equivalent to the content of that single dichroic pigment relative to the total mass of the liquid crystal composition. And, when the liquid crystal composition contains two or more dichroic pigments, the total content of the dichroic pigments is equivalent to the combined amount of those two or more dichroic pigments.

[0180] In a liquid crystal composition layer formed from a liquid crystal composition containing dichroic pigments, a state with high refractive index anisotropy to electromagnetic waves can be obtained. The exact reason for this is not yet clear, but it is speculated that by increasing the total content of dichroic pigments in the liquid crystal composition layer, the interaction between the dichroic pigments increases, thereby increasing the orientational order of the absorption axes caused by the absorption framework in the dichroic pigments. As a result, the absorption anisotropy of the dichroic pigments increases with the increase in refractive index anisotropy at wavelengths longer than the absorption wavelength.

[0181] Furthermore, from the viewpoint of achieving better results with the present invention, the total content of dichroic pigments in the liquid crystal composition is preferably 50% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, relative to the total mass of the liquid crystal composition. There is no particular upper limit, and examples include 100% by mass or less.

[0182] The radio wave control element of the present invention has been described in detail above. However, the present invention is not limited to the above examples. Various improvements and modifications can be made without departing from the spirit of the present invention.

[0183] Example The present invention will now be described in further detail based on embodiments. The materials, amounts, proportions, processing contents, and processing steps shown in the following embodiments can be appropriately modified without departing from the spirit of the invention. Therefore, the scope of the present invention should not be interpreted limitedly by the embodiments shown below.

[0184] Using optical simulation software, an image was created as follows: Figure 4 The model of the radio wave control element is shown. The simulation used COMSOL's finite element method simulation software "COMSOL Multiphysics".

[0185] [Example 1-1] The modeled radio wave control element is designed with a structure consisting of a second electrode, an intermediate layer, a liquid crystal composition layer, and a microstructure (metasurface structure) stacked sequentially. Furthermore, the size of a unit cell is set to 11 mm × 11 mm, and by applying periodic boundary conditions, the unit cells are arranged infinitely in the in-plane direction.

[0186] The second electrode and the microstructure are made of copper with a thickness of 2 μm. Furthermore, each microstructure is a square measuring 8 mm × 8 mm, positioned approximately at the center of the unit cell in the in-plane direction.

[0187] The liquid crystal composition layer is a composition formed by mixing liquid crystal compound 1-1 and liquid crystal compound 1-3 in a ratio of 50%:50%. Furthermore, the thickness of the liquid crystal composition layer is 300 μm.

[0188] A sample of a liquid crystal composition layer consisting of liquid crystal compound 1-1 and liquid crystal compound 1-3 was prepared. The maximum refractive index change per unit voltage in an electromagnetic wave with a wavelength range of 300 μm to 30 cm was measured by the above method, and the result was 0.12 (1 / V).

[0189] [Chemical Formula 3] [Chemical Formula 4] The intermediate layer is made of quartz (SiO2) and has a thickness of 300 μm. Therefore, the distance between the microstructure and the second electrode is 600 μm.

[0190] A sample with an intermediate layer made of quartz was prepared, and the maximum refractive index change per unit voltage in the range of 300 μm to 30 cm of electromagnetic waves was measured using the method described above. The result was 0.0001 (1 / V).

[0191] [Comparative Example 1-1] Without an intermediate layer, the thickness of the liquid crystal composition layer is set to 600 μm, and otherwise modeled as the same radio wave control element as in Example 1-1. That is, the distance between the microstructure and the second electrode is 600 μm.

[0192] [Comparative Examples 1-2] It lacks an intermediate layer and, otherwise, is modeled as the same radio wave control element as in Example 1-1. That is, the distance between the microstructure and the second electrode is 300 μm.

[0193] [evaluate] Using the simulation software "COMSOL Multiphysics", the 10GHz radio wave loss was calculated when a 10GHz radio wave was incident on and reflected from the radio wave control element models of the above-described embodiments and comparative examples. Furthermore, the radio wave loss in the liquid crystal composition layer is approximately the same regardless of the orientation state of the liquid crystal compound.

[0194] Furthermore, it is known that the switching time when applying a voltage to a liquid crystal composition layer to change the orientation state of the liquid crystal compound is proportional to the square of the thickness. The switching time in the radio wave control element of Comparative Example 1-1 was set to 1, and the switching times of the examples and comparative examples were calculated.

[0195] The results are shown in Table 1.

[0196] [Table 1]

[0197] As can be seen from Table 1, the embodiments of the present invention, compared with the comparative examples, can simultaneously shorten switching time and suppress radio wave loss.

[0198] [Example 2-1] The modeled waveguide-based radio wave control element is designed with a structure consisting of a waveguide, an intermediate layer, a liquid crystal composition layer, and a microstructure (metasurface structure) stacked sequentially. Furthermore, the waveguide is a copper metal waveguide with a width of 25.4 mm, a height of 12.7 mm, and a length of 80 mm, and three openings with a width of 13.7 mm and a length of 1 mm are arranged at 25 mm intervals on its upper surface.

[0199] The microstructure is made of copper and has a thickness of 2 μm. It is designed as a square with a size of 17 mm × 17 mm and is positioned directly above the opening on the upper surface of the waveguide.

[0200] The liquid crystal composition layer and the intermediate layer are the same as in Example 1-1. That is, the thickness of the liquid crystal composition layer is 300 μm, and the thickness of the intermediate layer is 300 μm. Therefore, the distance between the microstructure and the second electrode is 600 μm.

[0201] [Comparative Example 2-1] Without an intermediate layer, the thickness of the liquid crystal composition layer is set to 600 μm, and otherwise modeled as the same radio wave control element as in Example 2-1. That is, the distance between the microstructure and the second electrode is 600 μm.

[0202] [Comparative Example 2-2] It lacks an intermediate layer and, otherwise, is modeled as the same radio wave control element as in Example 2-1. That is, the distance between the microstructure and the second electrode is 300 μm.

[0203] [evaluate] Using the simulation software "COMSOL Multiphysics", the loss of 10 GHz radio waves emitted from the opening was calculated in the model of the radio wave control element of the above embodiments and comparative examples when a 10 GHz radio wave is incident on the waveguide and propagates.

[0204] The results are shown in Table 2.

[0205] [Table 2]

[0206] As can be seen from Table 2, the embodiments of the present invention, compared with the comparative examples, can both shorten the switching time and suppress radio wave loss.

[0207] Based on the above results, the effects of the present invention are obvious.

[0208] Symbol Explanation 2-Electronic wave reflecting device, 10, 50-Electronic wave control element, 12-Metasurface structure, 14-Microstructure (first electrode), 24-Support, 20-Liquid crystal composition layer, 26-Second electrode, 28-Power supply, 32-Intermediate layer, 52-Waveguide, 54-Opening, ANT-Antenna, AR1, AR2-Region, BL-Building, LC-Liquid crystal compound, RW-Electronic wave, UC-Unit cell.

Claims

1. A radio wave control element comprising a first electrode, a liquid crystal composition layer, and a second electrode, wherein, The radio wave control element has a metasurface structure composed of multiple microstructures arranged in a row. The metasurface structure constitutes at least a portion of the first electrode. An intermediate layer is provided between one of the first electrode and the second electrode and the liquid crystal composition layer, wherein the maximum refractive index change per unit voltage in the intermediate layer in the range of 300 μm to 30 cm is less than 0.001 (1 / V).

2. The radio wave control element according to claim 1, wherein the second electrode has a waveguide for guiding radio waves on the side opposite to the liquid crystal composition layer side, and the second electrode has an opening through which the radio waves pass.

3. The radio wave control element according to claim 2, wherein, The second electrode also serves as the waveguide.

4. The radio wave control element according to claim 1, wherein, The thickness of the intermediate layer is 0.1 to 2 times the thickness of the liquid crystal composition layer.

5. The radio wave control element according to any one of claims 1 to 4, which controls radio waves in the range of 300 μm to 30 cm.

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